Multi-layered wound dressing

ABSTRACT

A multi layered wound dressing comprising: (a) an adsorbent layer having high absorbency but low lateral wicking rate, and (b) a transmission layer having a high moisture vapor transmission rate overlying the side of said absorbent layer furthest from the wound.

CROSS-REFERENCE TO RELATED APPLICATIONS

This Application is a U.S. national phase application, filed under 35U.S.C. §371, of International Patent Application PCT/EP00/00132, whichwas filed on Jan. 7, 2000; and claims priority to Great BritainApplication No. 9900348, filed Jan. 9, 1999.

The present invention relates to a multi layered wound dressingparticularly, but not exclusively, for use as a dressing on highlyexudating wounds.

BACKGROUND OF THE INVENTION

It is known to make wound dressings for use on heavily exudating woundsfrom materials with a high moisture vapour transmission rate (MVTR).Such dressings rely on exudate being taken up by the dressing and spreadacross much of the surface area of the dressing in order to ensuresufficient moisture evaporation. Examples of such dressings are ALLEVYNmarketed in adhesive or non-adhesive versions by Smith and Nephew orTIELLE marketed by Johnson and Johnson. Such dressings are not designedto absorb and retain the exudate but manage the exudate by allowing themoisture present in the exudate to evaporate. A dressing said to have ahigh rate of moisture evaporation is described in EP 304 536A. Thedressing disclosed in this document has a flexible hydrophilic layerthat absorbs exudate, sandwiched between two layers of adhesive. Theabsorbent layer additionally contains a fabric layer which is intendedto improve the structural integrity of the dressing once it is exposedto exudate. A disadvantage of such dressings is that the lateral wickingof exudate is not contained and can cause normal skin surrounding thewound to macerate. A further disadvantage of such dressings is that therapid loss of exudate can cause the wound to desiccate.

EP-A 0538917 discloses a vented wound dressing is disclosed comprising athin conformable sheet material (12) at least a portion of the surfacearea of which it intended for placement as a dressing over a wound,which portion carries a pressure-sensitive adhesive coating (14) on onesurface thereof for adhering the dressing to skin, the coating beingapplied to provide repeating areas (16) of the sheet material containingno adhesive, at least a portion of the repeating areas of no adhesivehaving slits (18) extending through the thickness thereof to permittransfer or wound fluids through the sheet material unimpeded bypresence of adhesive material which can clog the slits and therebyinhibit fluid transfer therethrough.

There is thus a need for a wound dressing which is capable of absorbingexudate at the rate it is produced by a heavily exudating wound andwhich also does not cause maceration to the skin surrounding the woundthereby increasing the wear time of the dressing.

BRIEF SUMMARY OF THE INVENTION

We have now developed a multi layered wound dressing which alleviatesthe above problems and there is provided by a first embodiment of thepresent invention a multi layered wound dressing comprising:

(a) an absorbent layer having high absorbency but low lateral wicking;

(b) a transmission layer having a high MVTR overlying the side of saidabsorbent layer furthest from the wound.

We have found that wound dressings according to the invention maymitigate the problems associated with the management of high levels ofexudate produced by some wounds yet not induce maceration in the skinsurrounding the wound. It is thought that this is achieved by thecombined use of the absorbent layer with low lateral wicking, whichreadily absorbs exudate and transmits it to the transmission layer.

In a second embodiment of the invention the dressing further comprises ahigh lateral wicking layer between the absorbent and transmission layerswhich aids the spread of exudate across a greater area of the dressingbut away from the wound. In this way exudate is spread across a largesurface area to provide sufficient moisture vapour transmission but in alocation distant from the wound and skin. The passage of exudate throughthe dressing is therefore in a “T” shape where the lateral spread islimited in the absorbent layer and maximised in the transmission layer.Such a mechanism avoids maceration of the skin surrounding the woundsince the exudate is not contained in contact with the skin. As theabsorbent layer does however retain exudate in the immediate region ofthe wound, desiccation of the wound is avoided. This allows longer weartime for the patient and less disturbance of the wound on dressingchange.

A second embodiment of the invention of the present invention provides amulti layered wound dressing comprising:

(a) an absorbent layer having high absorbency but low lateral wicking;

(b) a transmission layer having a high MVTR overlying said absorbentlayer; and

(c) a spreading layer having high lateral wicking positioned between thetransmission and absorbent layers, the spreading layer overlying theside of the absorbent layer furthest from the wound.

The absorbent layer is present to transport wound fluid away from thewound and absorb it while containing lateral spread of exudate. By highabsorbency in the context of the present invention is meant anabsorbency of at least 10 g/g preferably from 15 g/g to 50 g/g and mostpreferably an absorbency of from 20 g/g to 50 g/g. By low lateralwicking is meant a lateral wicking rate of less than 20 mm/60 spreferably from 1 mm/60 s to 15 mm/60 s and most preferably a lateralwicking rate of from 1 mm/60 s to 10 mm/60 s. The absorbent layer ispreferably fibrous and most preferably comprises gel-forming fibres. Wehave found that fibrous layers as opposed to polymeric absorbent layershave the advantage that they are especially able to gel block whichresists the lateral spread of exudate. In addition exudate is absorbedrapidly and retained under pressure.

The fibres suitable for use in the absorbent layer of the presentinvention include hydrophilic fibres, which upon the uptake of woundexudate become moist and slippery or gelatinous and thus reduce thetendency for the surrounding fibres to adhere to the wound. The fibrescan be of the type, which retain their structural integrity onabsorption of exudate or can be of the type, which lose their fibrousform and become a structureless gel or a solution on absorption ofexudate.

The gel forming fibres are preferably spun sodium carboxymethylcellulosefibres, chemically modified cellulosic fibres, in particularcarboxymethylated cellulose fibres as described in PCT WO/9312275 toCourtaulds Plc or GB93/01258 to Courtaulds Plc, pectin fibres, alginatefibres and particularly those as described in WO94/17227 to E. R. Squibband Sons or EP 433354 to CV Laboratories Ltd or EP 476756 to CVLaboratories Ltd, or composite fibres of alginate and polysaccharidesuch as those described in EP 0892863 to Bristol-Myers Squibb Company,chitosan fibres, hyaluronic acid fibres, or other polysaccharide fibresor fibres derived from gums. The cellulosic fibres preferably have adegree of substitution of at least 0.05 carboxymethyl groups per glucoseunit. The production of solvent-spun cellulose fibres is described forexample in U.S. Pat. Nos. 4,246,221 and 4,196,281 as well as in PCTWO/9312275 mentioned above.

Preferably the gel forming fibres for use in the present invention havean absorbency of either water or saline of at least 15 g/g as measuredin the free swell absorbency method, more preferably at least 25 g/g or50 g/g. The degree of substitution of the gel forming fibre ispreferably at least 0.2 carboxymethyl groups per glucose unit, morepreferably between 0.3 and 0.5. The tenacity of the fibre is preferablyin the range 25-15 cN/tex.

The gel forming fibres are preferably mixed to give a dressingcomprising fibres of different absorbencies and also differentabsorbency rates and profiles. This can improve the strength andintegrity of the absorbent layer in a wet or moist state.

The absorbent layer may comprise other fibres such as textile fibreswhich can be natural or synthetic but are preferably cellulosic fibresfor example viscose rayon, multi-limbed viscose, cotton, or regeneratedcellulose or fibres having a higher absorbency than most textile fibressuch as the multi-limbed cellulose fibres as described in EP-A-301874.In general textile fibres absorb liquids by capillary action and are nothygroscopic this means that their absorbencies as measured by the freeswell absorbency test are low such as less than 1 gram of liquid pergram of fibre.

More preferably the dressing comprises an intimate blend of gel formingfibres and cellulosic fibres in the range of 50% to 95% of textilefibres and 5% to 50% of gel forming fibres by weight. Preferably thedressing comprises a blend of fibres in the range of 65% to 80% textilefibres and 20% to 35% gel forming fibres by weight and most preferably20% gel forming fibres and 80% textile fibres by weight.

The fibres suitable for use in the present invention can be processedusing conventional textile machinery, for example by the staple routeincluding cutting, carding and if desired crimping, drafting andspinning.

The spread layer of the present invention is preferably a net that has ahigh lateral wicking rate such as at least 30 mm/60 s, preferably 30mm/60 s to 60 mm/60 s. Preferably the net is viscose polyester net suchas that sold as scrim. Other nets made from composite plastic/viscosematerial, which are also hydrophilic, would also be suitable.

The transmission layer of the present invention is preferably a layerhaving a MVTR of at least 3000 g/m²/24 hours measured by the methoddescribed in 1993 BP Appendix XX J1 or in the range of from 1000 g/m²/24hours to 1000 g/m²/24 hours. The transmission layer may be in the formof film/foam laminate, for example expanded polyurethane foam laminatedto a polyurethane film.

The dressing may also comprise additional optional layers such as anadhesive layer for adhering the dressing to the skin surrounding thewound or a soluble medicated film applied to the wound contact layer foradministering a pharmaceutically active ingredient to the wound or anodour absorbing layer such as an activated carbon layer for reducing theodour from malodorous wounds. The adhesive layer may be applied to theside of dressing closest to the wound and may be provided withperforations to assist transport of exudate through the dressing. Theadhesive layer may also be applied to any of the other layers to providean island configuration.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Preferred embodiments of the present invention will now be described byway of example with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of one embodiment of a multi layered wounddressing according to the invention; and

FIG. 2 shows a sectional view of the dressing of FIG. 1 taken on theline AA.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to FIG. 1 of the drawings the multi layered dressingcomprises an absorbent layer (2), a spread layer (4) and a transmissionlayer (6). The absorbent layer is made from a 80/20 blend of cellulosefibres of the viscose rayon type with gel forming fibres such as thosedescribed in WO93/12275 to Courtaulds and sold as a fibrous dressing inthe product AQUACEL ex ConvaTec. The spread layer is a net with highlateral wicking capability such as OCD ex BSF non-wovens and thetransmission layer is a polyurethane foam/film laminate.

The dressing will typical y be made in three sizes, 55 mm×55 mm square,105×15 mm square and 205×105 mm rectangular, all dressings being about2.5 mm thick.

The dressing is placed on a wound, for example an ulcer, with theabsorbent layer in contact with the wound.

Wound dressings in accordance with the present invention may reducemaceration and provide a longer wear time than known dressings.

Preferred embodiments of the invention will now be illustrated in thefollowing examples.

EXAMPLE 1

A multi layered dressing according to the invention was made by blendingthe textile and gel-forming fibres in a 50/50 blend via mixing through apre-opener and carding machine. The blended fibres were thencross-folded to the correct density, approximately 100 g/m², andneedle-punched to provide appropriate tensile strength, at least 4N/cmfor the final non-woven absorbent layer. The various layers as describedfor the embodiment of the invention shown in

FIG. 1 were placed on top of one another and heat sealed together.

Optionally an adhesive was applied by extrusion in the correctdimensions onto silicone release paper and then transferred onto theabsorbent layer of the dressing, either prior to or subsequent to thelamination process. In this way the adhesive is keyed into the absorbentlayer via conventional pressure/heat lam-nation techniques.

The dressings were press cut or roller cut from the laminated web.

EXAMPLE 2

The MVTR of the dressing of Example 1 was measured as 750 g/m²/24 hr or1520 g/m²/48 hr.

The MVTR of a dressing according to Example 1 but with an absorbentlayer having an 80/20 blend of textile to gelling fibres was measured as600 g/m²/24 hr or 1410 g/m²/48 hr.

MVTR was measured via the BP method referenced above.

What is claimed is:
 1. A multi layered wound dressing which comprises:(a) an absorbent layer having a water absorbency of at least 10 g/g witha low lateral wicking rate (b) a transmission layer having a highmoisture vapor transmission rate overlying the side of said absorbentlayer furthest from the wound during use; and, (c) a spreading layerhaving high lateral wicking rate disposed between the absorbent andtransmission layer.
 2. The multi layered wound dressing as claimed inclaim 1 wherein the passage of exudate through the wound dressing has a“T”-shaped profile.
 3. The multi layered wound dressing as claimed inclaim 1, wherein the absorbent layer comprises a fibrous layer.
 4. Themulti layered wound dressing as claimed in claim 3 wherein the fibrouslayer comprises gel-forming fibres.
 5. The multi layered wound dressingas claimed in claim 1, wherein the spreading layer comprises a compositeplastic viscose net.
 6. The multi layered wound dressing as claimed inclaim 1, wherein the transmission layer comprises a foam.
 7. The multilayered wound dressing as claimed in claim 1, wherein the transmissionlayer has a moisture vapor transmission rate of at least 1000 g/m²/24hrs.
 8. The multi layered wound dressing as claimed in claim 1, furthercomprising an adhesive layer for adhering the multi layered wounddressing to the skin surrounding a wound.
 9. The multi layered wounddressing as claimed in claim 8 wherein the adhesive layer comprises ahydrocolloid based adhesive.
 10. The multi layered wound dressing asclaimed in claim 1, further comprising a film layer applied to the freesurface of the transmission layer.
 11. A method of treating orpreventing maceration of skin surrounding a wound, comprising: (a)providing multi layered a wound dressing comprising an absorbent layerand a transmission layer, wherein the wound dressing provides a “T”shaped profile to the passage of exudate through the wound dressing andwherein the absorbent layer exhibits a water absorbency of at least 10g/g; and, (b) contacting a wound with the wound dressing.
 12. A methodof treating or preventing maceration of skin surrounding a wound,comprising: (a) providing a wound dressing comprising (i) an absorbentlayer, wherein the absorbent layer exhibits a water absorbency of atleast 10 g/g and a low lateral wicking rate; (ii) a transmission layer,wherein the transmission layer exhibits a high moisture vaportransmission rate; and (iii) a spreading layer, wherein the spreadinglayer exhibits a high lateral wicking and wherein the spreading layer issandwiched between the absorbent layer and the transmission layer; and(b) contacting a wound with the wound dressing.
 13. A multi layeredwound dressing comprising: (a) an absorbent layer having a waterabsorbency of at least 10 g/g and a lateral wicking rate of less than 20mm/60 s; (b) a transmission layer having a moisture vapor transmissionrate of at least 1,000 g/m²/24 hrs overlying the side of said absorbentlayer furthest from the wound during use; and, (c) a spreading layerhaving a lateral wicking rate of at least 30 mm/60 s disposed betweenthe absorbent layer and the transmission layer.
 14. The multi layeredwound dressing of claim 13, wherein the passage of exudate through thewound dressing has a “T”-shaped profile.
 15. The multi layered wounddressing of claim 13, wherein the absorbent layer comprises a fibrouslayer.
 16. The multi layered wound dressing of claim 15, wherein thefibrous layer comprises gel-forming fibres.
 17. The multi layered wounddressing of claim 13, wherein the spreading layer comprises a compositeplastic viscose net.
 18. The multi layered wound dressing of claim 13,wherein the transmission layer comprises a foam.
 19. The multi-layeredwound dressing of claim 13, wherein the transmission layer has amoisture vapor transmission rate of at least 3,000 g/m²/24 hrs.
 20. Themulti layered wound dressing of claim 13, further comprising an adhesivelayer for adhering the multi layered wound dressing to the skinsurrounding the wound.
 21. The multi layered wound dressing of claim 20,wherein the adhesive layer is a hydrocolloid based adhesive.
 22. Themulti layered wound dressing of claim 13, further comprising a filmlayer applied to the free surface of the transmission layer.
 23. Amethod of treating or preventing maceration of skin surrounding a wound,comprising: (a) providing a wound dressing comprising (i) an absorbentlayer having a water absorbency of at least 10 g/g and a lateral wickingrate of less than 20 mm/60 s; (ii) a transmission layer having amoisture vapor transmission rate of at least 1,000 g/m²/24 hrs overlyingthe side. of said absorbent layer furthest from the wound during use;and, (iii) a spreading layer having a lateral wicking rate of at least30 mm/60 s disposed between the absorbent layer and the transmissionlayer; and (b) contacting a wound with the wound dressing.